Breeding is an important part of all livestock farming. Accurately detecting estrus, the period during which insemination should occur, is critical in order to maintain production and profit. However, conventional estrus detection depends on ocular inspection of the animals by skilled labour and this practice is expensive and relatively inefficient. Here, a wireless intravaginal probe for cattle capable of automatizing the process based on measurements of conductivity and temperature as well as movement sensing is presented and tested in-situ. These parameters can all be used independently to detect estrus. A good conformity between the data collected with this probe and established estrus patterns is demonstrated. Furthermore, the magnitude of natural daily variations and their impact on the individual parameters are discussed together with the impact of extraordinary events such as stress. Compared to existing alternatives, a multi-parameter approach like this is shown to be capable of much higher reliability, and also to be much more resistant to disturbances. The demonstrated system is very power efficient and capable of years of continuous isolated operation. Small to intermediate farm environments can be covered by the probe transmitters themselves with a single receiver unit, while bigger areas are handled with battery powered repeater units.